The present invention relates to a method of measuring the concentration of a leveler in a plating liquid that is used by a plating apparatus for filling metal such as copper in interconnection trenches and holes defined in the surface of a semiconductor substrate or the like, and a method of and an apparatus for managing a plating liquid to manage the components thereof.
For filling interconnection trenches and holes defined in the surface of a semiconductor substrate or the like according to a copper sulfate electroplating process, it is often customary to add three organic additives, described below, to basic plating liquid components copper sulfate (CuSO4.5H2O), sulfuric acid (H2SO4), and chlorine (Cl) in order to improve the qualities of a plated film and increase the fillability (embeddability) of trenches and holes.
One of the three organic additives is a carrier (also referred to as a brightener) for making the plated film dense and for increasing the luster of the plated film. The carrier generally comprises a sulfuric compound (e.g., HSxe2x80x94CnH2nxe2x80x94SO3 Mercapto alkylsulfonic acid) and exists as an anion in a plating liquid. The carrier obstructs the deposition of copper ions and promotes the achievement of a finer structure of the plated film.
The second of the three organic additives is a polymer (also referred to as a suppressor or a carrier) for suppressing the deposition of adsorbed copper ions on the surface of a cathode thereby to increase activated polarization for increased uniform electrodeposition. The polymer generally comprises a surface-active agent such as PEG or PPG.
The third organic additive is a leveler comprising a nitrogen-containing compound such as polyamine or the like. The leveler is present as a cation in a plating liquid.
The leveler is adsorbed greatly in a region where the current density is high. In the region where the adsorption of the leveler is large, an activation overvoltage increases to suppress the deposition of copper. At the bottom of fine trenches and holes, however, the adsorption of the leveler is smaller, resulting in a larger amount of the deposition of copper. The deposited state with the raised bottom represents an excellent leveling capability.
The management of the concentration of additives in a plating liquid of copper sulfate is important in managing the qualities of a plated film and the embeddability of trenches and holes. However, no process is presently available for measuring the absolute concentration of a trace of organic compound in a strong acid.
The present general process of analyzing the concentration of additives in a plating liquid is called a CV (Cyclic Voltammetric) process or a CVS (Cyclic Voltammetric Stripping) process. According to this process, the amount of copper deposited on a rotating cathode electrode is measured and converted into the concentration of an additive referred to as a deposition inhibitor or promoter.
In a plating solution of copper sulfate, however, only the concentrations of the carrier and the polymer can be measured by the above process, and the concentration of the leveler cannot be measured by the above process. The concentration of the leveler is the smallest among the concentrations of the above three additives. The leveler has properties similar to those of the polymer, and it has been said that it is impossible to measure the concentration of the leveler even according to the CV or CVS process.
A method of managing and adjusting the components of a plating liquid used by a plating apparatus of the type described above will be described below. Consumed amounts of the components of a plating liquid are empirically determined when the plating apparatus starts to operate in a plating mode and also when the plating apparatus is operating in a steady mode. Depending on a quantity of electricity (currentxc3x97time), an initial startup replenishing liquid (starter) is added to a base plating liquid. In a subsequent operation, a replenishing liquid (replenisher) is appropriately supplied to manage and adjust the components of the plating liquid. The starter comprises additive component liquids mixed depending on the consumed amounts of the components at the time of starting the plating apparatus. Similarly, the replenisher also comprises additive component liquids mixed depending on the consumed amounts of the components at the time of normal operation of the plating apparatus.
The empirical process has been used because it has been difficult to analyze the concentrations of the additives. However, since it is difficult to manage the concentrations accurately and the added amounts of the components are predetermined, this process finds it difficult to cope with a situation where the consumed amounts of the components are brought out of balance due to time-depending changes in the plating conditions.
There has recently been proposed an automatic analyzing device for quickly analyzing and automatically measuring additives according to an electrochemical process.
The present invention has been made in view of the above difficulties. It is an object of the present invention to provide a method of measuring the concentration of a leveler which is an additive in a plating liquid of copper sulfate, which has been impossible to measure according to a conventional CV or CVS process.
Another object of the present invention is to provide a method of and an apparatus for managing a plating liquid to automatically analyze additives of the plating liquid and adjust the components of the plating liquid based on the analyzed results.
In particular, a method of measuring the concentration of a leveler in a plating liquid of copper sulfate to measure the concentration of an additive containing nitrogen, which is referred to as a leveler, among organic additives contained in an electroplating liquid of copper sulfate is provided. The concentration of the leveler in the plating solution is determined based on a peak area (Ar value) in a peel-off region of the plating liquid measured according to a CV or CVS process.
Alternatively, a method of measuring the concentration of a leveler in a plating liquid of copper sulfate to measure the concentration of an additive containing nitrogen, which is referred to as a leveler, among organic additives contained in an electroplating liquid of copper sulfate is provided. The concentration of a brightener (carrier), and a wetting agent or a polarizing agent (polymer), which are other organic additives of the plating liquid, are analyzed. Thereafter, a calibration curve for the concentration of the leveler using a standard liquid prepared with the concentration of the carrier and the concentration of the polymer is generated. The concentration of the leveler of the plating liquid is determined based on a peak area (Ar value) in a peel-off region of the plating liquid measured according to a CV or CVS process.
As another alternative, a method of measuring the concentration of a leveler in a plating liquid of copper sulfate to measure the concentration of an additive containing nitrogen, which is referred to as a leveler, among organic additives contained in an electroplating liquid of copper sulfate is provided. A measuring liquid containing a promoting additive containing a sulfur-based material, which is referred to as a carrier, is prepared at a concentration that is 2 to 40 times a standard concentration. A difference in the amount of copper deposition on a rotary electrode according to a CV or CVS process is measured to calculate the concentration of the leveler.
The performance of the leveler in the plating solution of copper sulfate is not determined by the concentration of the leveler alone, but is affected by the concentrations of the carrier and the polymer. Particularly, the concentration of the carrier affects the leveling capability. If a nondye nitrogen compound such as polyamine or the like is used as the leveler, then the leveling nature becomes distinct, allowing a calibration curve to be drawn clearly, by increasing the concentration of the carrier in the plating liquid to be analyzed, relatively 2 to 40 times.
As another alternative, a method of measuring the concentration of a leveler in a plating liquid of copper sulfate to measure the concentration of an additive containing nitrogen, which is referred to as a leveler, among organic additives contained in an electroplating liquid of copper sulfate is provided. The plating liquid is passed through an organic anion-selective adsorption film to remove the promoting additive containing a sulfur-based material, which is referred to as a carrier, from the plating liquid. Thereafter, a difference in an amount of copper deposition on a rotary electrode is measured according to a CV or CVS process to calculate the concentration of the leveler.
If a nitrogen compound such as yanus green is used as the leveler, then the leveling nature becomes distinct, allowing a calibration curve to be drawn clearly, by bringing the amount of carrier closely to zero. Therefore, by passing the plating liquid through the organic anion-selective adsorption film, the carrier can be removed from the plating liquid, and a calibration curve can be drawn clearly.
Another method of managing a plating liquid includes sampling, at a predetermined interval, a predetermined amount of plating liquid in a plating apparatus which immerses a substrate to be plated in the plating liquid to plate a surface of the substrate. Components of the sampled plating liquid are analyzed with an automatic analyzing device, and component replenishing liquids comprising components of the plating liquid are supplied to the plating liquid based on analyzed results and/or the number of substrates to be plated and a quantity of electricity consumed to plate the substrates for thereby managing the components of the plating liquid. The component replenishing liquids comprise a standard liquid, a plurality of solutions of a basic liquid with a plurality of different additives added thereto, sulfuric acid, and hydrochloric acid, either wholly or partly, and the component replenishing liquids are supplied to the plating liquid for thereby individually replenishing and managing the components of the plating liquid.
In the above method, the basic liquid comprises a solution of at least copper sulfate (CuSO4.5H2O), and sulfuric acid (H2SO4), mixed at predetermined ratios. The standard liquid comprises a solution of the basic liquid, and the plurality of additives and hydrochloric acid added thereto at predetermined ratios.
A total amount of component replenishing liquids to be supplied to the plating liquid can be substantially the same as a reduction in the plating liquid which is caused by plating the substrate.
An apparatus is provided for managing the components of a plating liquid in a plating apparatus which immerses a substrate to be plated in the plating liquid in a plating tank to plate a surface of the substrates. The apparatus includes a plating liquid sampling device for sampling a predetermined amount of the plating liquid at a predetermined interval, an automatic analyzing device for automatically analyzing the components of the plating liquid sampled by the plating liquid sampling device, and a component replenishing liquid supply device for supplying component replenishing liquids comprising the components of the plating liquid. The component replenishing liquids are supplied to the plating liquid based on analyzed results from the automatic analyzing device and/or the number of substrates to be plated and a quantity of electricity consumed to plate the substrates for thereby managing the components of the plating liquid. The component replenishing liquids comprise a standard liquid, a plurality of solutions of a basic liquid with a plurality of different additives added thereto, sulfuric acid, and hydrochloric acid, either wholly or partly, and the component replenishing liquids are supplied by the component replenishing liquid supply device to the plating liquid for thereby individually replenishing and managing the components of the plating liquid.
In the above apparatus, the basic liquid comprises a solution of at least copper sulfate (CuSO4.5H2O), and sulfuric acid (H2SO4), mixed at predetermined ratios. The standard liquid comprises a solution of the basic liquid and the plurality of additives and hydrochloric acid added thereto at predetermined ratios.
The apparatus described above can include a plating liquid adjusting tank, separate from the plating tank, for supplying the component replenishing liquids to the plating liquid.